Blasting machines



p 1966 s. ASHWORTH ETAL 3,270,463

BLASTING MACHINES Filed Oct. 15, 1963 5 Sheets-Sheet 1 Sept. 6, 1966 s.l. ASHWORTH ETAL 3,

' BLASTING MACHINES Filed Oct. 15, 1963 5 Sheets-Sheet 2 vs v 'TOKS.

5 76mm? 7' Z353 1450010 girl S- l. ASHWORTH ETAL BLAS'IING MACHINESSept. 6, 1966 Filed Oct. 15, 1963 5 Sheets-Sheet 3 w 7'9 I 5 mum T'a HKT/ver flame? fin many 612,40) F/ew 7 preferably between 200 cylindricalportion United States Patent 3,270,463 BLASTING MACHINES Stewart IvesAshworth, Studley, and Anthony Gerard Field, Redditch, England,assignors to Abrasive Developments Limited, Henley-in-Arden, England, a

British company Filed Oct. 15, 1963, Ser. No. 319,088 Claims priority,application Great Britain, Oct. 16, 1962, 39,054/ 62 19 Claims. (Cl.51--8) This invention relates to a blasting machine having a blastingnozzle and means to supply abrasive to the nozzle.

An object of the invention is to provide an improved blasting machine inwhich the supply of abrasive to the blasting nozzle can easily andaccurately be controlled.

Accordingly, a blasting machine embodying the invention and having ablasting nozzle and means to supply abrasive to the nozzle ischaracterized in that said means include a container for abrasive, asieve in the container through which the abrasive passes to the nozzleas the container is vibrated, resilient means supporting the containerfor vibration, the container and the resilient means forming a systemhaving a fundamental resonant frequency, driving means for applyingpower to the system to cause it to vibrate at or adjacent to itsfundamental resonant frequency said driving means comprising an electricmotor mounted in the system and having a characteristic such that thespeed of the motor varies inversely as the load applied thereto and abob weight connected to the motor to be rotated eccentrically about agenerally horizontal axis and control means to vary the power input tothe electricmotor to control the amplitude of the vibration of thesystem at said resonant frequency and thus to control the rate of flowof abrasive through the sieve to the nozzle Preferably the container ismounted on a resilient elongated member which is anchored at one end toa support. The container may be mounted at one end of a spring boom, theother end of which is anchored to the support. The boom may be made ofwood for example, ash or Canadian fir; such wood is more resistant tofatigue than metal and has a low hysteresis loss.

The fundamental resonant frequency of the system is and 800 cycles perminute. An embodiment of the invention will now be described drawings,in which:

FIGURE 1 is an elevation of a blasting machine embodyingan inventionpartly in section and partly broken away to show the construction;

11. The column is steadied in position by means of a web 12. Bolted tothe top of the column 11 is a boom 13, one end of the boom beinganchored between the top of the column and a cover plate 14 and beingheld in position by bolts 15.

Mounted at the free end of the boom is a container indicated generallyat 16. The container comprises a 17 which is bolted at its lower end toan inverted frusto-conical portion 18. Secured in the top of thefrusto-conical portion 18 is a perforated metal plate 19 from the centerof which rises a tube 20 which opens at its lower end into thefrusto-conical portion 18.

The top of the tube 20 is provided with a gauze 21 to prevent abrasivematerial from passing down the tube 20.

FIGURE 1,the machine comprises a base at one side of which is mounted afixed column 45v 1 by way of example with reference to the accompanyingmatically operated valve and thence into an outlet pipe Patented Sept.6, 1966 Sandwiched between the perforated plate 19 and the lower edge ofthe cylindrical portion 17 is a nylon mesh sieve 22, the edges of thesieve being clamped between complementary flanges at the top of thefrusto-conical portion 18 and the bottom of the cylindrical portion 17,the flanges being clamped together by bolts 23.

The upper end of the container is provided with an inlet which has aspring loaded closure member 24 of substantially bell-shaped form. Afrusto-conical housing 25 is secured to the top plate 26 of thecontainer and spokes 27 in the housing 25 support a journal 28. Avertical rod 29 is slidable in the journal 28 and is secured at itslower end to the closure member 24. The rod 29 is provided with anoperating knob 30 at its upper end and a spring 31 is interposed betweenthe journal 28 and the knob 30. The plate 26 is provided with a recessaround the inlet in which is received an O-ring 32 which seals againstthe upper surface of the closure member 24 as shown in FIGURE 1.

The container is provided with a T-piece 33 at its lower end whichprovides an outlet. One side of the T-piece is connected to a dischargepipe 34 and the other side of the T-piece is connected to a compressedair line 35. The line 35 is fed from a main air line 36 which branchesat a T-piece 37 into the air line 35 and into another air line 38. Theair line 38 discharges into the top of the container through an elbow39.

Mounted on the container is a bracket 40 on which is bolted aseries-wound electric motor 41 carrying, on its driving spindle 42, aneccentric bob weight 43. The motor is controlled by means of a circuitwhich will be described hereinafter.

Referring now to FIGURE 3, the pneumatic circuit of the machine will nowbe described. The machine includes a compressor 44 which feeds air intoa line 45, the air being arranged to pass through a desiccator 46 to drythe air. Although a compressor has been shown as forming part of themachine it will be appreciated that the machine could be supplied by anoutside source of compressed air and would in fact probably be soconnected when used in surroundings where a number of blasting machineswere used and a central source of compressed air is provided.

The air line feeds to a junction piece 47 from which leads off in onedirection, the main air line 36 which feeds to the container 16 as hashereinbefor'e been described. The discharge pipe 34 passes through apneu- 48, thence into a T-piece 49 50 which feeds-the nozzle indicatedgenerally at 51. i

Another pipe 52 leads from the junction piece 47 through a pneumaticallyoperated valve 53 to the T-piece 49. A further service pipe 54 leadsfrom the junction piece 47 and branches at a T-piece 55 into branches 56and 57. The branch 56 leads to the valve 53 and the branch 57 leads tothe valve 48. Air flow through the branch 56 is controlled by a solenoidvalve 58 and air flow through the branch 57 is controlled by a solenoidvalve 59.

Referring now to FIGURE 2, the nozzle indicated generally at 51comprises a body 60 within which the outlet pipe 50 is received and issecured by means of an internal thread 61 in the body. Screwed into theend of the body 60 is a seal holder 62 in which is mounted a rubber seal63. A nozzle tube 64 has one end received in the seal 63 and is securedin position by means of a nozzle tube holder 65. The holder 65 isthreaded into the seal holder 62 and as the holder 65 is screwed intoposition it compresses the seal 63 which grips the nozzle tube 64.

Turning now to FIGURE 4, this shows the control means for the machine.Power for a machine is taken off the mains lines L1 and L2 and passesthrough a double pole mains switch S1. A fuse 66 is placed in line L1and a warning light 67 is connected between the lines L1 and L2 to showwhen the machine is in operation. Once the main switch S1 has beenclosed, the operation of the machine is controlled by two further footswitches S2 and S3.

A rectifier bridge 67 is connected between the lines L1 and L2 and hasoutput lines 68 and 69. Connected between the lines 68 and 69 is afurther line 70 in which is the foot switch S2 and the coil of anoperating relay R1.

Also connected between the lines 68 and 69 is a line 71 in which thereis arranged in series a tapped resistor 72, a variable resistor 73 and asecond tapped resistor 74. The line 75 tapped from the resistor 74passes through a relay contact ClRl of the relay R1 and through themotor 41 and a milli-ammeter 76a back to the line 69. Connected betweenthe line 75 and the line 69 is a capacitor 76.

The switch S3 is connected in a line 77 which extends between the linesL1 and L2 and this line also contains the solenoid 58$ for the solenoidvalve 58. A further line 78 extends between the lines L1 and L2 and thisline 78 contains a second contact C2R1 of the relay R1 and also thesolenoid 59S of the solenoid valve 59. A line 79 in parallel with thesolenoid 598 contains the coil of a time delay relay R2. A contact C1R2is connected between the variable tap 80 of the variable resistance 73and a line 81 leading to the junction between the resistors 73 and 74.

Operation of the machine is as follows, when the double pole switch S1is closed, current flows through the rectifier bridge 67 and along thelines 68, 69 through the resistors 72, 73 and 74 and charges up thecapacitor 76. If now it is desired to abrade a surface, the switch S2 isclosed in the line 74) and this energises the relay R1, and thus closesthe contacts ClRl and C2R1. As a result of the closing of the contactC1R1 the capacitor 76 discharges through the motor 41 so that a surge ofpower passes through the motor and the latter starts to rotate, thesurge assisting in overcoming the initial inertia of the bob weight 43.After the capacitor has discharged, the motor is supplied with voltagefrom the rectifier bridge 67 through the lines 68, the line 71, theresistors 72, 73 and 74, the line 75 the contact ClRl, the milli-ammeter76a and the line 69 back to the bridge 67.

The closing of the contact C2R1 in the line 78 energises the solenoid595 of the solenoid valve 59 and this allows air into the branch 57 thusopening the pneumatic valve 48 and allowing abrasive and air to passdown the discharge pipe 34 to the nozzle 51. Closing of the contact C2R1also energises the relay R2 and after a predetermined time delay therelay R2 closes the contact C1R2 thus connecting the variable tap 80 tothe junction between the resistors 73 and 74 so that variation of theposition of the tap 80 will vary the current supplied to the motor 41from the rectifier bridge 67. The tapped resistor 72 is pre-set to limitmaximum power supply to the motor and the pre-set resistor 74 is set tolimit the minimum power supplied to the motor. The maximum and minimumsupplies are chosen in accordance with the requirements of the machine.The relay R2 is preferably set so that the contact C1R2 is closedapproximately three seconds after the coil of the relay is energised.

Turning now to the operation of the boom and container, as the motorstarts to rotate with the bob weight the free end of the boom will startto vibrate generally vertically and as the motor gathers speed thevibrations will increase. The boom 13, the container 16 and the motor 41together with their associated brackets and parts attached to the boomform a system having a fundamental resonant frequency. The speed of themotor is so adjusted as to bring the system to vibrate at thisfundamental resonant frequency. The motor and the boom then look in whatis known as a dynamic couple, in this situation, the motor is rotatingso that the bob weight executes the V 34, through the v the pipe 52 tothe T-piece 49 and same number of rotary cycles as does the boomcomplete vibrations. That is to say the forces which are applied by theelectric motor and bob weight tend to keep the system vibrating at itsresonant frequency since the impulses given to the end of the boom arein phase with the vibrations executed by the boom. It has been foundthat if this condition is arrived at, small variations in the powerapplied to the motor will vary the amplitude of vibrations with noappreciable alteration in the speed of the motor. It is this discoverywhich is used in the present invention to control the amount of abrasivewhich is fed to the nozzle by varying the amplitude of vibration of thecontainer. Once the motor has got to its desired speed, the power inputthereto may be controlled by altering the variable tap on the variableresistor 73 and the result may be metered through the milli-ammeter 76a.

When the container is vibrating at the desired frequency, the abrasivein the cylindrical portion 17 will pass through the sieve 22 and theperforated plate 19 into the frusto-conical portion 18. The rate atwhich the abrasive will tflOW through the sieve depends upon theamplitude of vibration of the container. The abrasive falls from thefrusto-conical portion 18 into the T-piece 33 and the compressed airissuing from the pipe 35 entrains the abrasive and carries it down thedischarge pipe pneumatic valve 48, the T-piece 49, and the outlet pipeSil to the nozzle 51. The material passes through into the nozzle tube64 and is then directed on the article or surface to be abraded.

Since compressed air is supplied to both sides of the container bothabove and below the sieve the abrasive particles are not flowingdownwardly against a current of air and therefore do not tend to getelectrically charged and repelled. Moreover, the provision of the tube20 allows breathing between the upper and lower portions of thecontainer and reduces undesirable damping effects caused by the abrasiveabove the sieve tending to act as a piston.

When the abrading operation is finished the switch S2 is opened thusbreaking the circuit through the relay R1 and opening the contactsCI-R'l and C2R2. This stops the motor and de-energizes the solenoid 598of the solenoid valve 59 thus cutting olf the air supply to thepneumatic valve 48 and allowing this to close to prevent any further airand abrasive passing down the outlet pipe 50. If it is now desired toblow the abrasive away from the workpiece, the switch S3 is closed thusenergising the solenoid 583 of the solenoid valve 58 and allowing airinto the branch 56 to operate the pneumatic valve 53. The pneumaticvalve 53 opens and allows air to pass down then down the outlet pipe 50to the nozzle 51 where the air is discharged from the nozzle tube 64 andis used to blow away any excess abrasive. When it is desired to resumethe abrading operation, the switch S3 is opened thus de-energising the Isolenoid 58S closing the branch 56 and shutting the pneumatic valve 53.The switch S2 is then closed to start the motor and repeat the cycle ofoperations which has been described above.

The wood used for the boom must be of first quality, straight grainedand well seasoned. The resonant frequency of the boom is proportional toits thickness if the width is retained constant. As mentioned above thesystem comprising the container, the boom and the motor should bedesigned to have a fundamental resonant frequency of between 200 and800' vibrations per minute and a convenient value is 600 vibrations perminute.

The arrangement has the advantage that the motor will have a very 'longlife if it is sealed against the ingress of grit. Due to the fact thatthe motor is rotating the bob weight in phase with the vibrations of theboom, the load on the bearings of the motor, which maybe ball-bearings,is very small. Moreover, the speed of the motor is comparatively slow,these two features make for a long motor life.

The material in the desiccator 46 may be any conventional drying agentsuch as calcium chloride or silica gel. Alternatively the desiccator mayinclude a condenser. If an absorbent material is used it should bechanged regularly .and if a condenser is used means should be providedto run olf the accumulated condensate at frequent intervals. Asmentioned above, although a compressor is shown forming part of themachine the machine may be constructed to be connected to a compressorand if the latter has a desiccator then the provision of a desiccator onthe blasting machine will not be required.

The ratio of the cross-sectional areas of the nozzle tube 64 and theoutlet pipe 50 should not be too small or else the abrasive materialwill settle out in the pipe 50 and may thus cause a blockage. Even ifthe pipe 50 is not blocked the abrasive material may flow through thepipe in a slow, solid stream with little or no blasting power.

Conveniently the rectifying bridge 67 is arranged to supply voltage at apressure of 300 volts and the capacitor 7-6 may conveniently be of theorder of 60 microfarads. The time delay relay R2 is provided so thatfull power is not immediately applied to the motor 41. If full powerwere applied immediately the motor were started, the motor would tend torace and might well pass through the resonant frequency without forminga dynamic couple with the vibrations of the boom and locking in with thevibrations so that the movements of the bob weight are in phase with thevibrations of the boom.

It will be seen that the invention provides a blasting machine in whichthe amount of abrasive fed to the nozzle is easily controlled by meansof a variable resistor, in the emboidment described the resistor 73.Moreover the quantity can be controlled to a predetermined amount bycalibrating the milli-ammeter 76a so that a setting on the milli-ammeterwill correspond to a given amount of abrasive passing to the nozzle in aunit time.

What we claim then is:

1. A blasting machine including a blasting nozzle and means to supplyabrasive to the nozzle, said means including a container for abrasive, asieve in the container through which the abrasive passes as thecontainer is vibrated, resilient means supporting the container forvibration, the container and the resilient means forming forming asystem having a fundamental resonant frequency, driving means forapplying power to the system to cause it to vibrate at or adjacent toits fundamental resonant frequency, said driving means comprising anelectric motor mounted in the system and having a characteristic suchthat the speed of the motor varies inversely as the load applied theretoand a bob-weight connected to the motor to be rotated about a generallyhorizontal axis, control means to vary the power input to the electricmotor to control the amplitude of the vibration of the system at saidresonant frequency and thus to control the rate of flow of abrasivethrough the sieve and abrasive-conveying means connecting the containeron the output side of the sieve to the nozzle.

2. A blasting machine according to claim 1, including a support and aresilient elongated member which is anchored at one end to the support,the container being mounted on the member remote from the support.

3. A blasting machine according to claim 2 wherein the elongated memberis a wooden boom.

4. A blasting machine according to claim 3 wherein the boom is made of awood selected from the group consisting of ash and Canadian fir.

5. A blasting machine including a blasting nozzle and means to supplyabrasive to the nozzle, said means including a support, a resilient boomhaving a free end and anchored at its other end to the support, acontainer for abrasive mounted on the boom remote from its anchorage tothe support, a generally horizontal sieve in the container through whichabrasive passes as the container vibrates in a generally vertical plane,the boom and the container forming a system having a fundamentalresonant frequency, driving means for applying power to the system tocause it to vibrate at or adjacent to its fundamental resonantfrequency, control means to vary the power input to the driving means tocontrol the amplitude of vibration of the system at said resonantfrequency and thus to control the rate of flow of abrasive through thesieve, and pneumatic abrasive-conveying means connecting the containeron the output side of the sieve to the nozzle.

6. A blasting machine according to claim 5, wherein the containercomprises a chamber with an inlet for abrasive at the top thereof and anoutlet at the bottom thereof, the sieve being arranged transverse of thechamber between the inlet and the outlet.

7. A blasting machine according to claim 6, wherein a tube extendsupwardly from the sieve through the abrasive resting on the sieve andcommunicates at its ends with the parts of the chamber above and belowthe sieve.

8. A blasting machine according to claim 7 including a gauze at theupper end of the tube to prevent the passage of abrasive down the tube.

9. A blasting machine including a blasting nozzle and means to supplyabrasive to the nozzle, said means including a support, a resilient boomanchored at one end to the support, a container for abrasive mounted onthe boom remote from its anchorage to the support, an inlet for abrasiveat the top of the container, an outlet for abrasive at the bottom of thecontainer, a generally horizontal sieve in the container between theinlet and the outlet, the sieve allowing passage of abrasivetherethrough when the container is vibrated in a generally verticalplane, the boom and the container forming a system having a fundamentalresonant frequency, driving means for applying power to the system tocause it to vibrate at or adjacent to its fundamental resonantfrequency, control means to vary the power input to the driving means tocontrol the amplitude of vibration of the system at said resonantfrequency and thus to control the rate of flow of abrasive through thesieve, pneumatic abrasive-conveying means connecting the outlet of thecontainer to the nozzle, and a pressure equalising conduit connectedbetween the abrasive-conveying means and the upper end of the containerbetween the inlet and the sieve.

10. A blasting machine according to claim 9 includ ing a spring-loadedclosure member in the chamber inlet operable against the spring loadingto allow the feeding of abrasive into the container.

11. A blasting machine including a blasting nozzle and means to supplyabrasive to the nozzle, said means including a support, a resilient boomanchored at one end to the support, a container for abrasive mounted onthe boom remote from its anchorage to the support, a generallyhorizontal sieve in the container through which abrasive passes as thecontainer vibrates in a generally vertical plane, the boom and thecontainer forming a system having a fundamental resonant frequency, anelectric motor mounted on the boom adjacent to the container and havinga characteristic such that the speed of the motor varies inversely asthe load applied thereto, a bob-weight connected to the motor to berotated eccentrically about a generally horizontal axis, control meansto vary the power input to the motor to control the amplitude ofvibration of the system at said resonant frequency and thus to controlthe rate of flow of abrasive through the sieve, and pneumaticabrasive-conveying means connecting the container at the output side ofthe sieve to the nozzle.

12. A blasting machine according to claim 11, wherein the motor is aseries-wound electric motor.

13. A blasting machine according to claim 12 wherein the bob weight ismounted directly on the driving spindle of the electric motor.

14. A blasting machine according to claim 11, wherein the control meansincludes starting means arranged to provide an initial surge of powerthrough the motor to overcome the initial inertia of the bob weight.

15. A blasting machine according to claim 14, wherein the starting meansincludes a capacitor which is charged when power is applied to themachine and which dis charges through the motor to provide said initialsurge of power.

16. A blasting machine according to claim 11, wherein the control meanscomprises a variable resistor and a time-delay relay, the whole of theresistor initially being in the motor circuit upon starting the machinebut one end of the resistor being shorted to the variable tap thereof bythe time-delay relay after a predetermined time has elapsed from theapplication of power to the machine, the variable tap then controllingthe power fed to the motor.

17. A blasting machine including a blasting nozzle and means tosupply-abrasive to the nozzle, said means including a support, aresilient boom anchored at one end to the support, a container forabrasive mounted on the boom remote from its anchorage to the support, agenerally horizontal sieve in the container through which abrasivepasses as the container vibrates in a generally vertical plane, the boomand the container forming a system having a fundamental resonant'frequency of between 200 and 800 cycles per minute, driving means forapplyil'lg power to the system to cause it to vibrate at or adjacent toits fundamental resonant frequency, control means to vary the powerinput to the driving means to control the amplitude of vibration of thesystem at said resonant frequency and thus to control the rate of flowof abrasive through the sieve, and pneumatic abrasiveconveying meansconnecting the container at the output side of the sieve to the nozzle.

18. A blasting machine including a blasting nozzle and means to supplyabrasive to the nozzle, said means including a support, a resilient boomanchored at one end to the support, a container for abrasive mounted onthe boom remote from its anchorage to the support, a generallyhorizontal sieve in the container through which abrasive passes as thecontainer vibrates in a generally vertical plane, the boom and thecontainer forming a system having a fundamental resonant frequency ofbetween 200 and 800 cycles per minute, an electric motor mounted on theboom adjacent to the container and having a characteristic such that thespeed of the motor varies inversely as the load applied thereto, a bobweight connected to the motor to be rotated eccentrically about agenerally horizontal axis, control means to vary the power input to themotor to control the amplitude of vibration of the system as saidresonant frequency and thus to control the rate of flow of abrasivethrough the sieve and pneumatic abrasive-conveying means connecting thecontainer on the output side of the sieve to the nozzle.

19. A blasting machine including a blasting nozzle and means to supplyabrasive to the nozzle, said means including a support, a resilient boomanchored at one end to the support, a container for abrasive mounted onthe boom remote from its anchorage to the support, an inlet for abrasiveat the top of the container, an outlet for abrasive at the bottom of thecontainer, a generally horizontal sieve in the container between theinlet and the outlet, the sieve allowing passage of abrasivetherethrough when the container is vibrated in a generally verticalplane, the boom and the container forming a system having a fundamentalresonant frequency of between 200 and 800 cycles per minute, an electricmotor mounted on the boom adjacent to the container and having acharacteristic such that the speed of the motor varies inversely as theload applied thereto, a bob weight connected to the motor to be rotatedeccentrically about a generally horizontal axis, control means to varythe power input to the motor to control the amplitude of vibration ofthe system at said resonant frequency and thus to control the rate offlow of abrasive through the sieve, pneumatic abrasive-conveying meansconnecting the outlet of the container to the nozzle, and a pressureequalising conduit connected between the abrasive-conveying means andthe upper end of the container between the inlet and the sieve.

References Cited by the Examiner UNITED STATES PATENTS 671,410 4/1901Warren 51-12 2,433,684 12/1947 Damond 222196 X 2,618,109 11/1952 Miller51319 2,628,456 2/1953 Berg 51-8 2,725,684 12/1955 Crowe 51-8 3,149,4459/1964 Nolan 51-319 LESTER M. SWINGLE, Primary Examiner.

1. A BLASTING MACHINE INCLUDING A BLASTING NOZZLE AND MEANS TO SUPPLYABRASIVE TO THE NOZZLE, SAID MEANS INCLUDING A CONTAINER FOR ABRASIVE, ASIEVE IN THE CONTAINER THROUGH WHICH THE ABRASIVE PASSES AS THECONTAINER IS VIBRATED, RESILIENT MEANS SUPPORTING THE CONTAINER FORVIBRATION, THE CONTAINER AND THE RESILIENT MEANS FORMING FORMING ASYSTEM HAVING A FUNDAMENTAL RESONANT FREQUENCY, DRIVING MEANS FORAPPLYING POWER TO THE SYSTEM TO CAUSE IT TO VIBRATE AT OR ADJACENT TOITS FUNDAMENTAL RESONANT FREQUENCY, SAID DRIVING MEANS COMPRISING ANELECTRIC MOTOR MOUNTED IN THE SYSTEM AND HAVING A CHARACTERISTIC SUCHTHAT THE SPEED OF THE MOTOR VARIES INVERSELY AS THE LOAD APPLIED THERETOAND A BOB-WEIGHT CONNECTED TO THE MOTOR TO BE ROTATED ABOUT A GENERALLYHORIZONTAL AXIS, CONTROL MEANS TO VARY THE POWER INPUT TO THE ELECTRICMOTOR TO CONTROL THE AMPLITUDE OF THE VIBRATION OF THE SYSTEM AT SAIDRESONANT FREQUENCY AND THUS TO CONTROL THE RATE OF FLOW OF ABRASIVETHROUGH THE SIEVE AND ABRASIVE-CONVEYING MEANS CONNECTING THE CONTAINERON THE OUTPUT SIDE OF THE SIEVE TO THE NOZZLE.